Section 14 Power Supply Circuit
14.1
Overview
The H8/3887 Series incorporates an internal power supply step-down circuit. Use of this circuit
enables the internal power supply to be fixed at a constant level of approximately 1.5 V,
independently of the voltage of the power supply connected to the external VCC pin. As a result,
the current consumed when an external power supply is used at 1.8 V or above can be held down
to virtually the same low level as when used at approximately 1.5 V. It is, of course, also possible
to use the same level of external power supply voltage and internal power supply voltage without
using the internal power supply step-down circuit.
14.2
When Using the Internal Power Supply Step-Down Circuit
Connect the external power supply to the VCC pin, and connect a capacitance of approximately 0.1
µF between CVCC and VSS, as shown in figure 14-1. The internal step-down circuit is made
effective simply by adding this external circuit.
Notes: 1. In the external circuit interface, the external power supply voltage connected to VCC
and the GND potential connected to VSS are the reference levels. For example, for port
input/output levels, the VCC level is the reference for the high level, and the VSS level is
that for the low level.
2. When the internal power supply step-down circuit is used, operating frequency fosc
when VCC = 2.2 to 5.5 V is 0.4 MHz to 2 MHz. Otherwise, fosc is 0.4 MHz to 1 MHz.
3. The LCD power supply and A/D converter analog power supply are not affected by
internal step-down processing.
VCC
Step-down circuit
CVCC
Stabilization
capacitance
(approx. 0.1 µF)
Internal
Internal
power
logic
supply
VSS
Figure 14-1 Power Supply Connection when Internal Step-Down Circuit Is Used
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ETC [ ETC ]
